Motors are widely used in electronic and mechanical industries for converting electrical energy into mechanical energy. Generally, motors are classified into three types, for example DC motors, AC motors and stepper motors.
Stepper motors have precise positioning capability but generate relatively low power output. As a result, stepper motors often comply with the equipment requiring high positioning precision. For example, stepper motors are used to control zoom lenses of cameras. In comparison with stepper motors, DC motors and AC motors can provide more power output but lower positioning precision.
In other word, if high power output is required, DC motors and AC motors are usually used. Take electric punches for office use for example. For providing sufficient power to drive the punching knife of the electric punch, DC motors, universal motors or synchronous motors are generally used. When the procedure of punching through holes is terminated and the power provided by the motor is instantly interrupted (i.e. “a motor brake”), the punching knife needs to be precisely located at the return position. If the punching knife is deviated from the return position, the punching knife possibly blocks the insertion area of the electric punch and thus the documents fail to be placed in the insertion area.
Since the speed of the motor is not instantly reduced to zero when the power of the motor is eliminated, the punching knife may fail to be precisely located at the return position. In other words, due to an inertia swing phenomenon, the punching knife fails to stay at the return position and the punching knife is not be precisely located at the return position when the power of the motor is eliminated.
Furthermore, if high power output and high positioning precision are required, AC motors (e.g. induction motors) are usually used. The induction motors, however, may generate an inrush current during the motor brake is carried out. As a consequence, the components of the induction motors are readily damaged by the inrush current.
Therefore, there is a need of providing an improved motor driving system for providing high power output and high positioning precision to position a motor without the generation of a considerable inrush current.